1. Field
This disclosure relates generally to power conversion, and more specifically, to a power converter controller with stability compensation.
2. Description of Related Art
Many electronic devices such as cell phones, laptop computers, etc., use direct current (dc) power to operate. Conventional wall outlets generally deliver a high voltage alternating current (ac) power that needs to be transformed to dc power in order to be used as a power source by most electronic devices. Switched mode power converters are commonly used due to their high efficiency, small size, and low weight to convert the high voltage ac power to a regulated dc power. A switched mode power converter produces an output by periodically switching a power switch for one or more switching cycles.
A switched mode power converter may employ a controller to regulate output power delivered to an electrical device, such as a battery, which may be generally referred to as a load. The controller regulates power to the load by controlling a power switch to turn on and off in response to a feedback signal representative of the output of the power converter. In one example, the controller may use an on/off control technique to regulate an output of a switched mode power converter. In a typical on/off control technique, the controller decides whether to enable or disable the conduction of the power switch for each switching cycle by comparing the feedback signal with a threshold at the end of the previous switching cycle. For example, the controller may switch the power switch on (i.e., may initiate a switching activity) for the next switching cycle if the feedback signal is less than the threshold at the end of the previous switching cycle.
Switch mode power converters typically include an output capacitor to smooth out the ripple in the output voltage. The output capacitor may have a resistance associated with it that may be referred to as an equivalent series resistance (ESR). In some cases where the controller uses on/off control technique and the output capacitor has a small ESR, the feedback signal may not react quickly enough to the transfer of energy from the input to the output. For example, the feedback signal may not cross the threshold quickly enough after the power switch is switched off in a switching cycle such that the power switch is switched on too soon after the previous switching activity. This may lead to grouping of switching activity and result in unstable operation of the power converter.
Additionally, in some cases, noise may couple to the feedback signal such that the controller may not accurately detect the time that the feedback signal crosses the threshold. As a result, the controller may start mistiming the switching of the power switch which may lead to instability of the power converter.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present disclosure. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present disclosure.